Surgical needles are typically manufactured from various grades of metal steel alloys which will not corrode when the needles are exposed to ambient environmental conditions after manufacture and prior to, and during, use. The metal alloys typically may include the Type 300 and 400 series stainless steels and other conventional alloys such as Types 455, 420, and 420F, and the like. In addition, martensitic stainless steel alloys containing nickel and titanium are useful such as those disclosed in U.S. Pat. No. 5,000,912 which is incorporated by reference. Surgical needles and processes for manufacturing surgical needles are disclosed in commonly assigned, co-pending U.S. patent application Ser. Nos. 08/405,554 and 08/429,446 which are incorporated by reference.
In certain surgical procedures, it is preferred to utilize surgical needles having a blackened exterior surface rather than needles having a bright shiney surface. It is believed that blackening is caused by a build up of oxide on the surface of the metal alloy needle or instrument. There are a number of known conventional processes for blackening stainless steel alloys and other conventional metal alloys including various chemical and electrochemical processes. Processes for blackening surgical needles are disclosed in U.S. Pat. Nos. 4,959,068 and 4,905,695 which are incorporated by reference.
The conventional blackening processes which are most typically used are a chemical blackening treatment and an electrochemical treatment. The chemical treatment utilizes mixtures of acids and aqueous salts to oxidize the surface of a surgical needle thereby producing an oxidized layer and blackening the needle. For example, a typically used chemical mixture will contain sulfuric acid and potassium dichromate in an aqueous bath. The aqueous bath is preferably maintained at room temperature although other temperatures may be utilized. Another type of blackening treatment is an electrochemical process. In an electrochemical blackening process needles are placed in a chemical bath and an electric current is passed through the bath. Such electrochemical processes typically utilize voltages in the range of, for example, 30 volts to about 150 volts and high amperages in a range of, for example, about 5 amps to about 175 amps.
Although the existing electrochemical and chemical blackening processes produce needles having adequately blackened surfaces, there are certain disadvantages associated with the use of these processes. The processes require the use of chemical baths generating both chemical fumes and hazardous waste. The chemical baths have a limited useable life and have to be disposed of at considerable expense. In addition the use of the types of chemicals required for chemical or electrochemical baths has attendant safety hazards which must be constantly monitored. Also, the electrochemical process uses relatively high voltages and amperages and, once again, considerable safety precautions must be taken to protect operators.
Accordingly there is a need in this art for a novel method of blackening metal alloy surgical needles and surgical instruments without the use of chemical or electrochemical processes.